The present embodiments relate to a magnetic field generating device.
To perform magnetic resonance imaging (MRI), very powerful magnetic fields and electromagnetic alternating fields are generated in an MRI scanner in order to excite hydrogen nuclei. Image slices of the body of a patient are produced on the basis of the received electromagnetic fields. An MRI scanner includes a powerful magnet, which generates a steady-state magnetic field, gradient coils in X-, Y- and Z-direction with amplifiers, an RF transmitter and an RF receiver, which detects and amplifies an MR signal. Various computers are used for control and analysis.
To generate the steady-state magnetic field, a superconducting magnet is used. The electrical resistance of the superconducting magnet is reduced to zero by cooling to approximately 4 K so that the magnetic coil becomes superconducting. In practice, liquid helium, which is contained in a cryostat, is used as a coolant. Conventional MRI scanners therefore have a cavity (e.g., annular cavity), which is almost completely filled with liquid helium in order to keep the magnetic coils in the superconducting state. However, this has the disadvantage that a very large amount of helium (e.g., 1 m3) is used to fill the cavity. As helium tends to evaporate, the helium is regularly replenished, resulting in significant costs. Also, in many countries, a supply of helium in large quantities is difficult to obtain.